The present invention relates to a method and apparatus for treating a site contaminated with a hazardous substance. More particularly, the invention relates to a method and apparatus for microbiologically remediating soil and groundwater in a site contaminated with a hazardous substance.
Worldwide, the storage and transportation of hazardous substances requires countless tanks and pipelines. Substances typically processed in these facilities include petroleum distillates, industrial solvents, and industrial wastes. Due to the dangers presented by storing and transporting concentrated solutions of these materials, engineers and government agencies conduct extensive research and development to insure the tanks and pipelines used will effectively and safely contain these materials. Weathering and unforeseen engineering limitations, however, often cause the facilities to fail, resulting in the release of chemicals into the environment.
The failure of storage tanks and pipelines impacts on the physical and economic vitality of the contaminated area. The release of concentrated chemical solutions typically causes extensive damage to the local ecosystem by contaminating or killing indigenous plant and animal life. More remote ecosystems may be affected if the contamination migrates away from the site by entering a local groundwater flow. Further, local laws often require that the contaminated areas be remediated, and certified as such, prior to sale or rental of the contaminated property. These laws often result in land being left fallow for years or decades. In extreme cases, the inability to remediate contaminated sites renders industrial or residential areas uninhabitable, forcing owners and employees to evacuate the area.
Several methods are currently employed to biologically remediate sites contaminated with hazardous substances.
One approach to the bioremediation of contaminated sites involves the use of microorganisms indigenous to the subsurface environment. In particular, this technique involves supplying the indigenous microorganisms with gases and nutrients to increase their growth rate in situ. As the indigenous microbial population increases, more contaminant is oxidized. Once the contaminant is totally consumed, gas and nutrient supplies are terminated causing the microbial population to return to background levels. Exemplary of this technique are U.S. Pat. Nos. 3,846,290, 4,385,121, and 4,765,902. Although these methods achieve remediation over extended periods of use, the time required to build-up an effective in situ bioremediating culture at the contamination site creates a significant delay before effective treatment commences. Since delayed treatment permits the contaminant to remain in the ecosystem for a longer period of time, allowing additional migration and damage as a result, methods having inherent lag periods are less desirable.
Another method involves supplementing the indigenous microbial population with naturally occurring, or genetically altered, exogenous microorganisms. For example, if the primary area of contamination is within several centimeters of the ground surface, remediation is possible by discing or harrowing the area and then applying a solution containing nutrients and microorganisms. The inoculum grows by feeding on the nutrients and contaminants. Initial treatment, however, is often delayed because the contaminated area's toxicity kills a significant portion of the treating inoculum. Additional delays may result if the exogenous microbial population can not compete with indigenous populations. Once the microorganisms exhaust the food supply, i.e., the nutrients and contaminants, they perish leaving no lingering biological effects. U.S. Pat. No. 3,616,204 provides additional data and procedural aspects of this method.
Subsurface spills may also be remediated using a supplementary inoculum of microorganisms, however, the depth of the spill is problematic. In particular, because the contaminant's depth separates the remediating inoculum from needed air and nutrients, gas and nutrient supply systems become necessary. The relative closeness of the contamination to groundwater flows, as compared to surface spills, also necessitates expedited treatment of the contamination. To meet these requirements, Jhaveri U.S. Pat. No. 4,401,569 discloses a complex system of trenches, recirculation wells and gas injection wells, in combination with an above-ground treatment facility. Methods such as that disclosed in Jhaveri are effective if used for sufficient periods, however, the time required to construct the required trench systems creates an undesirable lag period before commencement of remediation. Additional delays also result if the treating microbial culture is killed or inhibited by toxic overloadings of the contaminant during the start-up phase. The efficacy of this technique is still further limited by engineering and safety limitations on trench depth.
Accordingly, it is an object of the invention to present a method and apparatus for the bioremediation of sites contaminated with hazardous substances.
It is a further object of the invention to present a method and apparatus capable of commencing bioremediation within a short period after arrival at a hazardous substance contaminated site.
It is yet another object of the invention to present a method and apparatus which is effective at ground level and at depths substantially below the ground surface.
It is yet a further object of the invention to present a method and apparatus which permits continual, efficient treatment of a contaminated site by protecting the treating microbial inoculum from toxic overloadings of the contamination, and generating an increased rate of remediation in the subsurface environment.